Interrogative sentences can be in positive or negative form, and in any tense.

What is the function of an interrogative sentence?

The basic function (job) of an interrogative sentence is to ask a direct question. It asks us something or requests information (as opposed to a statement which tells us something or gives information). Interrogative sentences require an answer. Look at these examples:

Is snow white? (answer → Yes.)

Why did John arrive late? (answer → Because the traffic was bad.)

Have any people actually met an alien? (answer → I don't know.)

How do we use an interrogative sentence?

We use interrogative sentences frequently in spoken and written language. They are one of the most common sentence types. Here are some extremely common interrogative sentences:

Indirect questions are not interrogative sentences

Direct question: Do you like coffee? This is an interrogative sentence, with the usual word order for direct questions: auxiliary verb + subject + main verb...

Indirect question: She asked me if I was hungry. This is a declarative sentence (and it contains an indirect question with no question mark). This sentence has the usual word order for statements: subject + main verb...